Embodiments of the present application relate to apparatus and methods for the plasma deposition of material on partially formed batteries.
Rechargeable batteries such as solid state and thin layer batteries are used to supply stored energy in many applications, including portable electronics, automobiles, cordless tool applications, medical devices, and even space systems. Thin layer rechargeable batteries have thin layers with thicknesses of less than 100 microns. Thin layer batteries are used in applications requiring a small size, high specific energy or energy density, and resistance to environmental degradation. Such solid state, thin layer batteries can have battery component layers that can include one or more current collectors, a cathode, an anode and an electrolyte, and which cooperate to store energy. One or more of the battery component layers, such as for example the electrolyte, cathode and anode, are composed of metal-containing materials that contain charge-carrying metal species that migrate during charging and discharging of the battery to store or release electrical energy.
The battery component layers are formed on the battery support by fabrication processes that include plasma processes, such as for example, sputtering, plasma-assisted evaporation, and plasma-enhanced CVD processes. In plasma processes, plasma ions and electrons in the plasma generate localized electrical fields on or near the exposed surface of the battery support. It has been discovered that when plasma processes are used to deposit material onto a partially fabricated battery cell, the localized electrical fields cause migration of the battery charge carrying metal ions within the battery component layers and from the underlying battery component layers of the battery cell to the exposed surface of the battery cell. The accumulated ions result in precipitated elemental metals and metal compounds on the exposed surface of the battery cell, and metal ion depleted regions in the battery cell, all of which reduce battery performance.
As one illustrative example, in lithium batteries, some of the battery component layers are composed of a lithium-containing material such as lithium metal oxide or lithium-containing compound. For example, the cathode can be composed of lithium cobalt oxide, the electrolyte of lithium phosphorus oxynitride, and the anode of elemental lithium. When a partially fabricated battery cell is exposed to the plasma, the resultant surface electrical field drives lithium ions to move inside, or in and out of, the lithium containing materials. The resultant depletion of lithium ions caused the electrical properties of underlying and sputtered layers to degrade during the sputtering process. For example, the cathode of lithium cobalt oxide had substantially lower efficiencies when depleted of lithium ion. Lithium precipitated in the electrolyte layer or on the electrolyte layer surface also degraded electrolyte quality.
For various reasons that include these and other deficiencies, and despite the development of various battery fabrication processes and apparatus, further improvements in the plasma processing of battery component layers are continuously being sought.